1. Field of the Invention
The present invention relates to a profiled plastic band for the production of wound pipes having a helically extending seam, which band includes two parallel side edges each having one respective longitudinal flange of which one forms a web and the other includes a longitudinally extending groove such that in the wound condition of the pipe the grooves embraces a section of a web allocated thereto and inserted thereinto.
2. Description of the Prior Art
The production of plastic pipes by helically winding a plastic band of the kind described above is known and disclosed for instance in the U.S. Pat. No. 3 199 541 or the DE-PS No. 17 78 201.
One of the problems of pipes produced by such a procedure is the reliable locking of the seam, i.e. the maintaining of the seam lock in the desired operational position (also during operation, e.g. in the case of pressurized pipes).
It thus has been proposed to weld or glue the cooperating areas of the seam. Such solutions could, however not always satisfy the demands made, specifically regarding the sealing properties. This difficulty has been solved partly by complicated solutions such as, e.g. insertion of additional sealing members, which led, however, to new difficulties during welding.
A further solution has among other been proposed by the present applicant, according to which the mechanical locking of the seam has been secured by means of a separate closing band which engages over the mutually bordering edges of the band or edge flanges and is supported against further ribs of the band.
This solution is technically convincing, indeed, but involves a certain additional expenditure (the additional closing band).